The massively parallel nature of information processing in neural systems calls for an accurate sensing and recording of the electrical activity of many neurons simultaneously and in-vivo. Until now, this has been possible with both tethered and, to a limited extent, untethered solutions in mammals, but not in insects. The fundamental limitations were size and weight of neural probes. Our proposal calls for the development of nanoscale neural probes based on photonic crystal (PC) nanocavity lasers that can be used for untethered neural sensing and recording in-vivo. The probes will be optically powered and capable of transmitting measured signals at pre-specied wavelengths. An array of such probes operating at hundreds to thousands of dierent wavelengths will allow one to record and analyze massive amounts of neural activity in parallel and in real-time. The probes will include an electric field sensor that modulates either the output power or the center wavelength of an optically pumped PC nanocavity laser. Both the sensor and the nanocavity laser will be integrated into a III-V group compound semiconductor membrane that will be fabricated in a modern nanofabrication process. This process will enable a low-cost production of tens of thousands of novel devices in parallel. As our testbed, we will use the early olfactory system of the fruit fly Drosophila Melanogaster. When inserted at the base of a sensillum on the fly's antenna, the probe will pick up the local eld potential generated by 2-4 olfactory sensory neurons projecting their dendrites into that sensillum. This local field potential will then be encoded into a lightwave emitted by the nanocavity laser on the probe. Finally, an optical data acquisition system will be used to capture the lightwave and decode the local field potential. Combined with an already-developed system for precise odorant delivery and measurement as well as theoretical advances in neural system identication, an array of such untethered probes will give us an exceptionally detailed insight into how odorants are represented by olfactory sensory neurons both in time and space and will aid in developing a deeper understanding of odor signal processing in higher brain centers. Furthermore, we plan to monitor the neural activity of olfactory sensory neurons in freely moving ies in a natural environment. An array consisting of 20 to 30 nanoprobes will be inserted into the antennae and monitored in free ight. Given the extraordinarily small size and weight, flexible functionality and low cost of nanofabricated semiconductor probes, we also envision them being used for untethered neural sensing and recording in a wide variety of sensory and motor systems of both vertebrates and invertebrates.